Ketoconazole, 1-acetyl-4-[4-[[2-(2,4-diehlorophenyl)-2-[(1H-imidazol-1-yl)-methyl]-1,3-dioxolan-4-yl] methoxy] phenyl] piperazine, is a racemic mixture of the cis enantiomers (−)-(2S, 4R) and (+)-(2R, 4S) marketed as an anti-fungal agent. Ketoconazole inhibits fungal growth through the inhibition of ergosterol synthesis. Ergosterol is a key component of fungal cell walls.
More recently, ketoconazole was found to decrease plasma cortisol and to be useful, alone and in combination with other agents, in the treatment of a variety of diseases and conditions, including type 2 diabetes, Metabolic Syndrome (also known as the Insulin Resistance Syndrome, Dysmetabolic Syndrome or Syndrome X), and other medical conditions that are associated with elevated cortisol levels. See U.S. Pat. Nos. 5,584,790; 6,166,017; and 6,642,236, each of which is incorporated herein by reference. Cortisol is a stress-related hormone secreted from the cortex of the adrenal glands. ACTH (adenocorticotropic hormone) increases cortisol secretion. ACTH is secreted by the pituitary gland, a process activated by secretion of corticotropin releasing hormone (CRH) from the hypothalamus.
Cortisol circulates in the bloodstream and activates specific intracellular receptors, such as the glucocorticoid receptor (GR). Disturbances in cortisol levels, synthetic rates or activity have been shown to be associated with numerous metabolic complications, including insulin resistance, obesity, diabetes and Metabolic Syndrome. Additionally, these metabolic abnormalities are associated with substantially increased risk of cardiovascular disease, a major cause of death in industrialized countries. See Marin P et al., “Cortisol secretion in relation to body fat distribution in obese premenopausal women.” Metabolism 1992; 41:882-886, Bjorntorp, “Neuroendocrine perturbations as a cause of insulin resistance.” Diabetes Metab Res Rev 1999; 15(6): 427-41, and Rosmond, “Role of stress in the pathogenesis of the metabolic syndrome.” Psychoneuroendocrinology 2005; 30(1): 1-10, each of which is incorporated herein by reference.
While ketoconazole is known to inhibit some of the enzymatic steps in cortisol synthesis, such as, for example, 17α hydroxylase (Wachall et al., “Imidazole substituted biphenyls: a new class of highly potent and in vivo active inhibitors of P450 17 as potential therapeutics for treatment of prostate cancer.” Bioorg Med Chem 1999; 7(9): 1913-24, incorporated herein by reference) and 11b-hydroxylase (Rotstein et al., “Stereoisomers of ketoconazole: preparation and biological activity.” J Med Chem 1992; 35(15): 2818-25) and 11β-hydroxy steroid dehydrogenase (11β-HSD) (Diederich et al., “In the search for specific inhibitors of human 11β-hydroxysteroid-dehydrogenases (11β-HSDs): chenodeoxycholic acid selectively inhibits 11β-HSD-I.” Eur J Endocrinol 2000; 142(2): 200-7, incorporated herein by reference) the mechanisms by which ketoconazole decreases cortisol levels in the plasma have not been reported. For example, there is uncertainty regarding the effect of ketoconazole on the 11β-hydroxysteroid dehydrogenase (11β-HSD) enzymes. There are two 11β-HSD enzymes. One of these, 11β-HSD-I, is primarily a reductase that is highly expressed in the liver and can convert the inactive 11-keto glucocorticoid to the active glucocorticoid (cortisol in humans and corticosterone in rats). In contrast, the other, 11β-HSD-II, is primarily expressed in the kidney and acts primarily as an oxidase that converts active glucocorticoid (cortisol in humans and corticosterone in rats) to inactive 11-keto glucocorticoids. Thus, the plasma concentration of active glucocorticoid is influenced by the rate of synthesis, controlled in part by the activity of adrenal 11β-hydroxylase and by the rate of interconversion, controlled in part by the relative activities of the two 11β-HSD enzymes. Ketoconazole is known to inhibit these three enzymes (Diederich et al., supra) and the 2S,4R enantiomer is more active against the adrenal 11β-hydroxylase enzyme than is the 2R,4S enantiomer (Rotstein et al., supra). However, there are no reports describing the effect of the two ketoconazole enantiomers on either of 11β-HSD-I or 11β-HSD-II, so it is not possible to predict what effects, if any, the two different ketoconazole enantiomers will each have on plasma levels of the active glucocorticoid levels in a mammal.
Ketoconazole has also been reported to lower cholesterol levels in humans (Sonino et al. (1991). “Ketoconazole treatment in Cushing's syndrome: experience in 34 patients.” Clin Endocrinol (Oxf). 35(4): 347-52; Gylling et al. (1993). “Effects of ketoconazole on cholesterol precursors and low density lipoprotein kinetics in hypercholesterolemia.” J Lipid Res. 34(1): 59-67) each of which is incorporated herein by reference). The 2S,4R enantiomer is more active against the cholesterol synthetic enzyme 14αlanosterol demethylase than is the other (2R,4S) enantiomer (Rotstein et al infra). However, because cholesterol level in a human patient is controlled by the rate of metabolism and excretion as well as by the rate of synthesis it is not possible to predict from this whether the 2S,4R enantiomer of ketoconazole will be more effective at lowering cholesterol levels.
The use of ketoconazole as a therapeutic is complicated by the effect of ketoconazole on the P450 enzymes responsible for drug metabolism. Several of these P450 enzymes are inhibited by ketoconazole (Rotstein et al., supra). This inhibition leads to an alteration in the clearance of ketoconazole itself (Brass et al., “Disposition of ketoconazole, an oral antifungal, in humans.” Antimicrob Agents Chemother 1982; 21(1): 151-8, incorporated herein by reference) and several other important drugs such as Glivec (Dutreix et al., “Pharmacokinetic interaction between ketoconazole and imatinib mesylate (Glivec) in healthy subjects.” Cancer Chemother Pharmnacol 2004; 54(4): 290-4) and methylprednisolone (Glynn et al., “Effects of ketoconazole on methylprednisolone pharmacokinetics and cortisol secretion.” Clin Pharmacol Ther 1986; 39(6): 654-9). As a result, the exposure of a patient to ketoconazole increases with repeated dosing, despite no increase in the amount of drug administered to the patient. This exposure and increase in exposure can be measured and demonstrated using the “Area under the Curve” (AUC) or the product of the concentration of the drug found in the plasma and the time period over which the measurements are made. The AUC for ketoconazole following the first exposure is significantly less than the AUC for ketoconazole after repeated exposures. This increase in drug exposure means that it is difficult to provide an accurate and consistent dose of the drug to a patient. Further, the increase in drug exposure increases the likelihood of adverse side effects associated with ketoconazole use.
Rotstein et al. (Rotstein et al., supra) have examined the effects of the two ketoconazole cis enantiomers on the principal P450 enzymes responsible for drug metabolism and reported “ . . . almost no selectivity was observed for the ketoconazole isomers” and, referring to drug metabolizing P450 enzymes: “[t]he IC50 values for the cis enantiomers were similar to those previously reported for racemic ketoconazole”. This report indicated that both of the cis enantiomers could contribute significantly to the AUC problem observed with the ketoconazole racemate.
One of the adverse side effects of ketoconazole administration exacerbated by this AUC problem is liver reactions. Asymptomatic liver reactions can be measured by an increase in the level of liver specific enzymes found in the serum and an increase in these enzymes has been noted in ketoconazole treated patients (Sohn, “Evaluation of ketoconazole.” Clin Pharm 1982; 1(3): 217-24, and Janssen and Symoens, “Hepatic reactions during ketoconazole treatment.” Am J Med 1983; 74(1B): 80-5, each of which is incorporated herein by reference). In addition 1:12,000 patients will have more severe liver failure (Smith and Henry, “Ketoconazole: an orally effective antifungal agent. Mechanism of action, pharmacology, clinical efficacy and adverse effects.” Pharmacotherapy 1984; 4(4): 199-204, incorporated herein by reference). As noted above, the amount of ketoconazole that a patient is exposed to increases with repeated dosing even though the amount of drug taken per day does not increase (the “AUC problem”). The AUC correlates with liver damage in rabbits (Ma et al., “Hepatotoxicity and toxicokinetics of ketoconazole in rabbits.” Acta Pharmacol Sin 2003; 24(8): 778-782 incorporated herein by reference) and increased exposure to the drug is believed to increase the frequency of liver damage reported in ketoconazole treated patients.
Additionally, U.S. Pat. No. 6,040,307, incorporated herein by reference, reports that the 2S,4R enantiomer is efficacious in treating fungal infections. This same patent application also reports studies on isolated guinea pig hearts that show that the administration of racemic ketoconazole may be associated with an increased risk of cardiac arrhythmia, but provides no data in support of that assertion. However, as disclosed in that patent, arrhythmia had not been previously reported as a side effect of systemic racemic ketoconazole, although a particular subtype of arrhythmia, torsades de pointes, has been reported when racemic ketoconazole was administered concurrently with terfenadine. Furthermore several published reports (for example, Morganroth et al. (1997). “Lack of effect of azelastine and ketoconazole coadministration on electrocardiographic parameters in healthy volunteers.” J Clin Pharmacol. 37(11): 1065-72) have demonstrated that ketoconazole does not increase the QTc interval. This interval is used as a surrogate marker to determine whether drugs have the potential for inducing arrhythmia. U.S. Pat. No. 6,040,307 also makes reference to diminished hepatoxicity associated with the 2S,4R enantiomer but provides no data in support of that assertion. The method provided in U.S. Pat. No. 6,040,307 does not allow for the assessment of hepatoxicity as the method uses microsomes isolated from frozen tissue.
Thus, there remains a need for new therapeutic agents and methods for treating diseases and conditions associated with elevated cortisol levels or activity or that may be treated by lowering cortisol level or activity that are as effective as ketoconazole but do not present, or present to a lesser degree, the issues of drug interactions and adverse side effects of ketoconazole. The present invention meets these and other needs.